Thermostat for fire alarm systems



Jan. 17, 1933. J JQHNSQN 1,894,746

THERMOSTAT FOR FIRE ALARM SYSTEMS Filed Nov. 14, 1929 IN VEN TOR.

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Patented Jan. 17, 1933 UNITED STATES JOHN M. JOHNSON, OF KANSAS CITY, MISSOURI THERMOSTAT FOR FIRE ALARM SYSTEMS Application filed Hoveznber 14, 1929. Serial No. 497,110.

This invention relates to improvements in thermostats for fire alarm systems and refers more particularly to a thermostat arrangement which may be interposed in a fire alarm system having separate fire alarm and trouble alarm circuits.

The thermostat is adapted for use in fire alarm systems such as those described in my co-pending application Serial No. 29%,346, filed July :21, 1928.

Among the salient objects of the invention are to provide an improved type of thermostat which is equipped with spring circuit interrupters consisting of spring leaves beneath which are positioned compressed coil springs; which doubly assure the interruption of he circuit on melting or failure of the fusible material which unites the contacting elements. Another feature of the invention is the enlarged surface of the spring contacting leaves which increases the absorption. The shape of the contacting members which are united by the fusible element assures positive union of the contacting parts while permitting instant release on failure of the fusible material due to heat.

Fig. 1 is a perspective view of the thermostat, showing one of the contactleaves in released position.

Fig. 2 is a bottom view with part of the casing broken away to expose the binding posts.

Fig. 3 is a central sectional view of the thermostat.

Referring to the drawing, the thermostat consists of an insulator or porcelain element 1 to the bottom of which is aflixed a metallic casing 2 by means of a central screw 3. Holes in the casing shown at 4 permit the same to be attached to the walls or ceiling of a building, or the casing may be entirely inset in the wall or ceiling of the building so that only the porcelain portion of the thermostat is exposed. In case the thermostat is inset so that only the porcelain por ion is exposed the circuit wires are led in through the holes l, while in installations in which the thermostat is not inset, the circuit wires.

are threaded through the side apertures produced by stamping in portions of the side wall as shown at 5 to produce the apertures or holes 6.

Extending through the insulated base element 1 are four binding posts 6 to which the circuit wires are attached by means of nuts 7. Two of the heads of the screws 6 which serve as binding posts hold in position the receivers 8 which consist of a base portion, an upstanding member and a top parallel to the base which has side flanges or upturned portions 8. The heads of the other two screws 6 which serve as binding posts hold the members 9 fixedly in the troughs or grooves formed in the porcelain base to prevent dis placement of the components which serve as t interrupters.

The members 9 have a flat metallic base, a hollow spring cylinder 9 and knife edge supports 9" to which the upstanding portion of the spring leaf conforms when the leaves are sprung into contact relation with the spring receivers 8. The spring leaf circuit interrupters also have a bottom base portion 10 which is doubled back beneath the base of the member 9. An upstanding or vertical portion 10 lies adjacent the support member 9 and the free end of the spring is united with the top of the adjacent spring receiver by a fusible metal when the circuit is closed, and spings bacl: to a position shown in Fig. 1 and Fig. 3 when the holding metal has been fused. When fused and one of the springs released a single circuit is opened and a trouble alarm is registered at the recording station. \Vhen both springs are released by fusing of the metal and both circuits opened a fire alarm signal is recorded.

Coil springs 1 are compressed within the cylind '9 when the circuit is closed and the spring l af contacted with the spring receiver. hese coil springs 11 furnish a double assurance that the circuit will be interrupted and an alarm recorded when the fusible metal is melted or fails for any reason.

The spring leaf contact elements have an enlarged surface, each covering substantially one-half of the exposed surface of the porcelain base. This increase in the exposed surface gives more rapid heat and heat absorption and increased sensitiveness and rapidity of action to the contact spring, as the heat is more rear ily conducted to the fusible material. The fusion of the upturned edges 8 on the top of the receivers is to produce a better soldering union between the two contacting elements by means of the fusible metal. lhese flanges do not, however, in any way affect the release of the spring leaves.

To prevent corrosion of the coil spring 11, the spring leaf is hermetically sealed to the top of the cylinder 9 when the circuit is closed or the leaf incontacting relation with the spring receiver. This sealing is effect-ed by placing a sealing substance on the underneath portion of the spring when the spring is open and subsequently uniting the spring and spring receiver by means of a fusible metal of predetermined melting point. lVhen the spring leaf is united with the spring receiver, the under surface of the spring will contact the top of the cylinder 9 so that the sealing substance will hermetr .cally seal against corrosion the springs contained in the spring cylinders.

It is recognized that heretofore thermostats and fusible links have been used as circuit interrupters in fire alarm systems, but it is considered as new practice to utilize a double circuit interrupter operating trouble alarm and fire alarm circuits which devices are equipped with trouble spring release, one spring constituting the leaf contacting element and the other an auxiliary coil spring hermetically sealed therebeneath. The particular design of the spring leaves with their enlarged surfaces and the shape of the contacting elements at the contacting pointare considered as other novel features.

I claim as my invention:

1. A closed circuit thermostat for double circuit fire alarm systems comprising an insulated base, connections thereon for interposing the thermostat into the system, spring leaf circuit interrupters uniting the connections and held under tension by solder of predetermined melting point, and auxiliary coil springs hermetically sealed beneath the circuit interrupters providing double assurance for interrupting the circuit by melting or release of the fusible metal.

2. A closed circuit thermostat for double circuit fire alarm systems comprising an insulated base, connections thereon for interposing the thermostat into the system, fiat topped receivers having upturned edges connected to the circuits, and spring leaf circuit interrupters having enlarged heat absorption surfaces also connected into the circuits adjacent the receivers and having portions thereof fitting the the contactlng areas of the receivers, said conass gns tacting areas united by solder of predetermined melting point. i

8. A closed circuit thermostat for double circuit fire alarm systems comprising an insulated base, connections thereon for interposing the thermostat into the system, receivers with upturned edges connected to the circuits, and spring leaf circuit interrupters the extremities of which are held in the depressed portions of the receivers by solder of a predetermined melting point.

4. A closed circuit thermostat for double circuit fire alarm systems comprising an insulated base, connections thereon for interposing the thermostat into the system, receivers with upturned edges connected to the circuits, spring leaf circuit interrupters the extremities of which are held in the depressed portions of the receivers by solder of a predetermined melting point, and encased coil springs beneath the interrupters under compression when the circuits are closed.

5. A closed circuit thermostat for double circuit fire alarm systems comprising an insulated base, connections thereon for interposing the thermostat into the system, receivers with upturned edges connected to the circuits, spring leaf circuit interrupters the extremities of which are held in the depressed portions of the receivers by solder of a predeterminedmelting point, and encased coil springs hermetically sealed beneath the interrupters and held under compression when the circuits are closed.

In testimony whereof I affix my signature.

JOHN M. JOHNSON. 

